1. Field of the Invention
This invention relates to crystalline silicates having a high silica/alumina mole ratio of greater than about 1600 and little or no acid activity. In one aspect of this invention a novel catalytic composition is prepared from said high silica materials by reacting the same with certain binders such as an alumina-containing binder and in another aspect of this invention conversion processes are carried out with said novel catalytic composition.
2. Description of the Prior Art
High silica/alumina mole ratio crystalline silicates are well known in the art and it is generally accepted that the ion exchange capacity of such crystalline silicates is directly dependent on the amount of metal which is tetrahedrally coordinated with the silica in the framework. Thus, for example, with regard to the most common zeolitic crystalline materials; namely, crystalline aluminosilicate zeolites, such material can be described as a rigid three dimensional network of SiO.sub.4 and AlO.sub.4 in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of total aluminum and silicon atoms to oxygen is 1:2. The electrovalence of the tetrahedra-containing aluminum is balanced by the inclusion in the crystal of a cation. Quite obviously, the more aluminum that is present in the crystal the more cations can be introduced into the crystalline structure. Recently, the scientific and technical literature has disclosed high silica-containing zeolitic structures wherein substantially all or a portion of the aluminum present in the crystal framework has been replaced by other metals either partially or completely. Thus, for example, iron, chromium and boron are materials which have been described in the prior art as capable of being substituted for aluminum in the crystal framework and quite obviously, the ion exchange capacity of the resulting zeolitic structure will again be determined by the amount of metal which is in tetrahedral coordination with the silica. Thus, for example, the more boron there is in a crystalline structure, the more cations are required to balance the electronegativity thereof and when such cations are of the acidic type, such as hydrogen, they impart tremendous catalytic activity to the crystalline material. On the other hand, crystalline silicates having a high silica/alumina mole ratio of greater than about 1600 have many important properties and characterisitcs and have a high degree of structural stability such that they have become candidates for use in various processes, incuding catalytic processes. Materials of this type are well known in the art and include high silica-containing aluminosilicates such as ZSM-5 (U.S. Pat. No. 3,702,886), ZSM-11 (U.S. Pat. No. 3,709,979), and ZSM-12 (U.S. Pat. No. 3,832,449) to mention a few. It is also known in the art that the silica/alumina ratio of a given zeolite is often variable. For example, zeolite X can be synthesized with a silica/alumina ratio of from 2 to 3 and zeolite Y from about 3 to about 6. In some zeolites, the upper limit of silica/alumina ratio is virtually unbounded. Zeolite ZSM-5 is one such material wherein the silica/alumina ratio is at least 5. U.S. Pat. No. 3,941,871 discloses a crystalline metallo-aluminosilicate essentially free of aluminum and exhibiting an X-ray diffraction pattern characteristic of ZSM-5. U.S. Pat. Nos. 4,061,724; 4,073,865; and 4,104,294 describe microporous crystalline silicas wherein the aluminum content is present at very low levels. Because of the extremely low aluminum content of these high silica-containing zeolites their ion exchange capacity is not as great as materials with a higher aluminum content. Therefore, when these materials are contacted with an acidic solution and thereafter are processed in a conventional manner, they are not as catalytically active as their higher aluminum containing counterparts. This invention permits the preparation and use of certain high silica-containing materials which have all the desirable properties inherently possessed by such high silica materials and yet have an acid activity which has heretofore only been possible to be achieved by materials having a higher aluminum content in their "as synthesized" form or by certain activation techniques, such as treatment with metallic vapors.